Red Lion GEMINI 33 - Manual (Page 21)

GEMINI 3300 20 MA CURRENT LOOP COMMUNICATIONS
The Gemini 3300’s 20 mA Current Loop Communications Option allows a
“two-way” serial communications link to be established in order to monitor
or change the counter values, Presets and Scale Factor from a remote location.
Some typical devices that can be connected with the Gemini 3300 are: a
printer, terminal, programmable controller, or host computer. For devices
that use RS232, a GCM232 Serial Converter Module is available to convert
the 20 mA Current Loop signals to RS232 and vice-versa.
There are two loops that must be established. One for sending commands to
the Gemini 3300 and one for receiving the data values from the Gemini 3300.
Up to sixteen Geminis or other RLC units with 20 mA serial communication
capability, can be connected together in the “loop” if a 24 V external current
source is utilized. A maximum of seven units can be installed in the loop if the
Gemini’s 20 mA current source is used. The units are assigned addresses by
setting the Serial DIP Switches on each unit. The applications can be as
simple as attaching a printer to obtain hard copy of the display information or
as involved as using a host computer to automatically set up Presets and Scale
Factors on a number of Geminis.
With the Communications Option, the following functions can be performed:
1. Interrogation of the Count Values, Presets, and Scale Factor.
2. Changing of the Count Values, Presets and Scale Factor.
3. Resetting of the Count Values and Outputs.
4. Changing the viewed display value.
5. Automatic print-out when using a printer and the “Print Request”
Terminal.
COMMUNICATION FORMAT
Data is sent by switching off and on the current in the 20 mA current loop.
Data is received by monitoring the switching action and interpreting the
codes that are transmitted. In order for data to be interpreted correctly, there
must be identical formats and Baud Rates.
The format that the Gemini 3300 will accept is: 1 start bit, 7 data bits, 1
odd parity bit, and 1 stop bit. The Baud Rates that are available are: 300,
600, 1200 and 2400.
The selection of the Baud Rate is done by setting DIP switches. Refer to the
“Current Loop Installation” section, for set-up instructions.
SENDING COMMANDS & DATA TO THE GEMINI 3300
When sending commands to the Gemini 3300, a command string must be
constructed. The command string may consist of command codes, value
identifiers, and numerical data. Following is a list of commands and value
identifiers that are used when communicating with the Gemini 3300.
COMMAND DESCRIPTION
N (4EH) Address command; followed by a one or 2 unit address
number 1-15 and one of the following commands.
D (44H) Change display command; followed by E, F, or G. This
command changes the viewed display channel on the
Gemini 3300 to “P” (Process Counter), “B” (Batch
Counter), or “T” (Total Counter).
P (50H) Transmit per Print Options command.
R (52H) Reset command; followed by a value identifier (E, F, or
G); operates on Process, Batch or Total Counter. A value
identifier of M: resets counter(s) currently selected in
Code 61.
T (54H) Transmit Value command; followed by a value identifier
(A-G); operates on counter values, Presets and Scale Factors.
V (56H) Change Value command; followed by a value identifier
(A-G); operates on count values, Scale Factor, and Presets.
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FIG. 1: DATA FORMAT-10 BIT FRAME [300, 600, 1200, 2400 Baud]